Coating method and apparatus employing rotating workholder



Jan. 10, 1967 Filed May 27, 1963 L. A. FLACCHE COATING METHOD AND APPARATUS EMPLOYING ROTATING WORKHOLDER 2 Sheets-Sheet l INVENTOR LOUIS A. FLACCHE Q 9 IILTIU 22 ls V l' x W: A

FIG-l VACUUM l PUMP 22 18 FIGA Q M/Jw ATTORNEYS Jan. 10, 1967 L. A. FLACHE 3,297,475

COATING METHOD AND APPARATUS EMPLOYING ROTATING WORKHOLDER F1166 llay 27, 1983 2 ShBBtS-ShBEt 2 INVENTOR LOUIS A.FLAC.CHE

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ATTORNEYS United States Patent 3,297,475 COATING METHOD AND APPARATUS EMPLOY- ING ROTATING WORKHOLDER Louis A. Flacche, Audubon, N.J., assignor to The New York Air Brake Company, a corporation of New Jersey Filed May 27, 1963, Ser. No. 283,373 Claims. (Cl. 117106) This invention relates to a method and apparatus for uniformly coating a convex spherical surface and more particularly, to a method and apparatus in which the spherical surface is simultaneously rotated about three different axes during the coating operation.

Up to this time, the most satisfactory device for uniformly coating convex spherical surfaces consisted of a complex yoke arrangement in which the arms of the yoke span the poles of the spherical surface to be coated. The yoke and surface rotate about one axis while the surface is simultaneously rotated about its polar axis. However, in this arrangement, the area around the poles is exposed to the coating zone longer than the remaining area and thus, in order to achieve a uniform coating, it is necessary to incorporate into the device means to increase the rotational speed of the yoke as it approaches the coating zone.

The object of this invention is to provide an improved method and apparatus for uniformly coating convex, spherical surfaces. According to the invention, the surface to be coated is supported by a workholder and both the workholder and surface are rotated simultaneously about three different axes during the coating operation. It has been found that the degree of coincidence between the center of the surface to be coated and the center of the workholder has a direct bearing on the degree of uniformity of the coating thickness. If the centers coincide, a completely uniform coating will result, because every point on the surface to be coated crosses, in a given time interval, an imaginary straight line between the common center of the surface and the center of the evaporator or source, the same number of times and at the same speed.

Of course, the degree of coincidence between the centers is only as critical as the permissible tolerance on the uniformity of the coating thickness and if the tolerance is liberal, then the coincidence need not be exact.

The preferred embodiment of the invention is described in detail with reference to the accompanying drawing in which:

FIG. 1 is a side view of the preferred apparatus of this invention for simultaneously coating two identical spherical surfaces in a vacuum environment.

FIG. 2 is a top view of the preferred apparatus with one of the workholders removed.

FIG. 3 is a sectional view, on enlarged scale, taken on line 3-3 of FIG. 2.

FIG. 4 is a sectional view taken on line 4-4 of FIG. 1.

Referring to FIG. 1, the coating apparatus of this invention is enclosed by a bell 11 which is mounted on the base 12. The interior of the bell 11 is connected to a vacuum pump 13. A plate 14 is supported above the base by a plurality of filament posts 15. This plate 14 is formed with a large, slightly off-center hole 16.

A conventional evaporator source 17 and its associated mask 18 are positioned between the plate and the base by two pairs of posts 19 and 21, respectively, which depend from the plate. The position of the mask 18 with respect to the source 17 and the configuration of the aperture 22 in the mask vary with the coating process involved and for any given process, the position of the mask and the configuration of the aperture required will be apparent to those skilled in the art.

The workholding mechanism 23 is supported above the plate 14 by the bracket 24-. This mechanism 23, more clearly shown in FIG. 2, includes a drive shaft 25 journalled in the bearing member 26 and rotatably driven by conventional means, not shown. The shaft 25 is attached at one end to the disc 27 and passes through, but is not connected to, a stationary pulley 28, positioned between the member 26 and the disc 27. Mounted eccentrically on the disc is a bearing 29. A flexible cable 31 is journalled in this bearing and is connected at one end to the pulley 32. This pulley is rotatably mounted on one end of the bearing 29 and is coupled with the stationary pulley 28 by means of a belt 33. The cable 31 extends from the other end of the bearing and is housed in the hollow, tubular support 34 attached to the disc.

As shown more clearly in FIG. 3, the other end of the cable 31 is connected to the hub assembly 35. In addition to the hub 36, this assembly comprises a rubber-edged wheel 37 which is non-rotatably attached to the end of support 34 and an idler wheel 38, similar to wheel 37, which is carried by the hub. It should be noted that the support 34 is curved so that the center of the hub assembly 35 remains, at all times, on the extended center line of the shaft 25. Also, the wheels 37 and 38 are positioned so as to be symmetrically located about the center of the hub assembly.

The hub includes two posts 39 and 41 which project from the center of opposite sides of the hub. Each post carries an identical workholder 42 that freely rotates about the post. The workholders include a disc 43 and an encircling flange 44 adjacent the discs periphery. There is a cup-like recess 45 formed in the center of each disc. The posts 39 and 41 project through a hole in the center of this recess and carry at their outer ends the fastening means 46 which biases the workholders toward the hub. As shown in FIG. 1, the workholders are mounted so that the hub assembly 35 is received in these recesses. Thus, when assembled, the edges of the wheels 37 and 38 are in frictional engagement with the annular serrated zone 47 formed on the bottom of the recess. Finally, it should be noted that when the workholders 42 are assembled, the centers of the spherical surfaces attached thereto will, as nearly as possible, coincide with the center of the hub assembly. Of course, it should be obvious that, if two true hemispheres are coated on this apparatus, exact coincidence of the centers of these hemispheres and the center of the workholders 42 is impossible. However, as stated above, if the centers of the hemispheres and the center of the workholder are made to coincide as closely as possible, a relatively uniform coating can be achieved. The apparatus shown in the preferred embodiment is adapted to coat two hemispheres and the closest that the centers of hemispheres can be to the center of the workholder is one-half the thickness of the cable 31 and support 34 plus running clearance. However, even with this difference a satisfactory coating can be obtained.

Operation Before commencing the coating operation, the bell 11 is removed and a hemisphere is securely mounted on each of the workholders. The large diameter portion of the hemisphere, indicated by phantom lines 40 and 49', snugly fits around the flange 44 and abuts the outer peripheral portion of the disc 43. After the hemispheres have been mounted, the bell is replaced and its interior space evacuated by the pump 13. The workholding mechanism 23 is started, the evaporator source 17 is heated and the coating operation proceeds in the normal manner, thereby coating the outer surfaces of the hemispheres with a coating having a variation in thickness of a few angstroms. The advantage provided by this invention lies in the fact that during any specified time interval, every point on the outer surfaces of the hemispheres will cross an imaginary line between the common center of the hemispheres and hub assembly and the center of the evaporator source the same number of lines and at the same speed.

This advantage is obtained through the use of the Workholding mechanism 23 which simultaneously rotates the hemispheres about three different axes. When the mechanism is operating, the shaft 25 causes the disc 27 to rotate at a constant speed. Since the disc carries the support 34 and thus, the hub assembly 35, and the workholders 42, with the hemispheres mounted thereon, rotation of this disc causes these above-mentioned elements to rotate about an axis which coincides with the center line of shaft 25,

As the disc 27 rotates, the cable 31 rotates about its own axis in addition to rotating with the disc. This is due to the fact that as the pulley 32 revolves about stationary pulley 28, it is rotated about its own axis because of the belt coupling between the two pulleys. Thus, the' hub 36, the workholders 42 and the hemispheres are also rotated about the axis of the cable 31. Moreover, as the workholde'rs rotate about the axis of the cable they engage the wheel 37. Since this wheel does not rotate about the axis of the cable, this engagement causes the two Workholders to be rotated in opposite directions about the posts 39 and 41. Thus, in this manner, the hemispheres are simultaneously rotated about three different axes.

It should be apparent from the drawings that the hemispheres do not rotate about each of the three axes at the same speed, although rotational speed about each axis is constant. The ratios of the rotational speeds used on the above described embodiment were selected because they provided satisfactory results, but many other ratios could have been chosen. By way of example, and not of limitation, it has been found that if the workholders rotate about the axis of the flexible cable at a speed approximately 1.3 times the speed of the drive shaft and if the Workholders rotate about the posts on the hub at a speed approximately 1.8 times the speed of the drive shaft, satisfactory results can be achieved with a drive shaft speed of from to 50 rpm.

It should also be apparent that it is not necessary to coat two hemispheres at the same time and that by modifying the workholder, other spherical surfaces, i.e., surfaces less than or greater than a hemisphere, could be coated. Moreover, in certain coating applications in which the tolerance on the thickness of the coating is liberal, the mask is not required. Finally, it should be obvious that the practice of this invention is not limited to a vacuum environment, and in fact, has many diverse applications.

As stated previously, the drawings and description relate only to the preferred embodiment of the invention. Since many changes can be made in the structure of this embodiment without departing from the inventive concept, the following claims should provide the sole measure of the scope of this invention.

What I claim is:

1. The method of coating a convex spherical surface with auniform thickness of material comprising the steps of simultaneously rotating the surface about its center in three different directions and projecting the coating mate rial onto said surface while it rotates.

2. The method of coating a convex spherical surface with a uniform thickness of material comprising the steps of simultaneously rotating said surface about its center in three different directions so that in a certain time interval, every point on said surface will have crossed a selected imaginary straight line which includes the center of said surface the same number of times and at the same velocity and directionally projecting the coating material onto said surface while it rotates.

3. Apparatus for coating a convex spherical surface with a uniform thickness of material comprising (a) a workholder for supporting said surface;

(b) means spaced from said surface for projecting the coating material onto said surface; and

(c) means for simultaneously rotating said surface about its center in three different directions.

4. The apparatus recited in claim 3 in which (a) the projecting means includes a mask;

(b) said surface is no greater than a hemisphere;

(c) the center of the workholder and the center of said surface substantially coincide; and

(d) the means for rotating is arranged so that in a certain time interval, every point on said surface will have crossed an imaginary straight line between the common center of the workholder and surface and the center of the projecting means the same number of times at the same velocity.

5. The apparatus recited in claim 4 in which (a) the projecting means includes an evaporator; and

(b) the projecting means, Workholder, rotating means,

and surface are enclosed in an evacuated housing during the coating operation.

References Cited by the Examiner UNITED STATES PATENTS 1/1961 Friedman et a1. 18-26 X 1/1963 Miller 1826 

1. THE METHOD OF COATING A CONVEX SPHERICAL SURFACE WITH A UNIFORM THICKNESS OF MATERIAL COMPRISING THE STEPS OF SIMULTANEOUSLY ROTATING THE SURFACE ABOUT ITS CENTER IN THREE DIFFERENT DIRECTIONS AND PROJECTING THE COATING MATERIAL ONTO SAID SURFACE WHILE IT ROTATES.
 3. APPARATUS FOR COATING A CONVEX SPHERICAL SURFACE WITH A UNIFORM THICKENSS OF MATERIAL COMPRISING 